# Radiometric dating half life problems

### Calculating Half-Life - Chemistry LibreTexts

Radioactive elements "decay" (that is, change into other elements) by "half lives." If a half life is equal to one year, then one half of the radioactive element will. Half Life. As we learned yesterday radioactive elements decay at Because its half-life is so long it is useful for dating the oldest rocks on Earth, but not very. A radioactive half-life refers to the amount of time it takes for half of the To answer this question, there is no need to solve for the radioactive decay equation .

Be sure to define the following words with the class: Discuss the possible uses of radioactive material in science. BBC Bitesize goes on to explain radioactive dating in the following sectionthough it is only text and images, without an interactive video. Introduce the MEA lesson concept: Your students' help has been requested by the Natural History Foundation in order to help them select the proper elemental isotopes to use in their radioactive dating process.

### Radioactive Dating: Half-Life & Geologic Time -

The students must decide which elemental isotope is best suited for determining the absolute age of one of three ancient discoveries. Inform students that they will be completing a full essay written response with their decisions and reasoning at the end of this project.

Arrange students in groups of to prepare for the project it may be helpful to have predetermined groups ready. Allow students in each group to read the client letter. This is an excellent time to also show the students the provided image. Some of the problems associated with K-Ar dating are Excess argon. This is only a problem when dating very young rocks or in dating whole rocks instead of mineral separates.

Minerals should not contain any excess Ar because Ar should not enter the crystal structure of a mineral when it crystallizes.

Thus, it always better to date minerals that have high K contents, such as sanidine or biotite. If these are not present, Plagioclase or hornblende.

• 5.7: Calculating Half-Life

If none of these are present, then the only alternative is to date whole rocks. Some 40Ar could be absorbed onto the sample surface. This can be corrected for. Most minerals will lose Ar on heating above oC - thus metamorphism can cause a loss of Ar or a partial loss of Ar which will reset the atomic clock.

If only partial loss of Ar occurs then the age determined will be in between the age of crystallization and the age of metamorphism. If complete loss of Ar occurs during metamorphism, then the date is that of the metamorphic event.

### ChemTeam: Half-Life Problems #1 - 10

The problem is that there is no way of knowing whether or not partial or complete loss of Ar has occurred. Thus the ratio of 14C to 14N in the Earth's atmosphere is constant. Living organisms continually exchange Carbon and Nitrogen with the atmosphere by breathing, feeding, and photosynthesis.

When an organism dies, the 14C decays back to 14N, with a half-life of 5, years. Measuring the amount of 14C in this dead material thus enables the determination of the time elapsed since the organism died.

Radiocarbon dates are obtained from such things as bones, teeth, charcoal, fossilized wood, and shells. Because of the short half-life of 14C, it is only used to date materials younger than about 70, years.

## Radioactive Dating: Half-Life & Geologic Time

Other Uses of Isotopes Radioactivity is an important heat source in the Earth. Elements like K, U, Th, and Rb occur in quantities large enough to release a substantial amount of heat through radioactive decay.

Thus radioactive isotopes have potential as fuel for such processes as mountain building, convection in the mantle to drive plate tectonics, and convection in the core to produce the Earth's magnetic Field.